In most instances, in the past, because of the number of steps required to assemble and the number of parts required for constructing measuring instruments of the moving coil type such as D'Arsonval meters, such meters have not been as capable of mass production manufacture as the meter of the present invention. Typically, in the past, such meters have required precision assembly, with the attendent use of expensive jigs and fixtures, and have frequently required extensive calibration after assembly. In most instances, the assembly and calibration included selecting a scale which matched the characteristics of the meter, after these characteristics were observed and determined by testing each meter.
Frequently, the need of such tedious calibration and precise manufacture and assembly tolerances, was the result of a meter arrangement where tolerances accumulated so the assembled meters in some instances were quite accurate, and in other instances were exceedingly inaccurate. Even though the usual accuracy of a relatively low cost meter is plus or minus 2% of fully scale deflection, it was frequently impossible to maintain accuracy at a 4% or 5% level. Correspondingly, rejects were quite common, and a reasonably accurate low cost meter was not available.
U.S. Pat. No. 3,764,909, mentioned previously discloses a meter which can be mass produced, provides the desired accuracy, and can be rapidly assembled. The meter disclosed herein, while incorporating some of the features of U.S. Pat. No. 3,764,909, includes many unique additional features which provide fo rapid and inexpensive assembly and manufacture, with a minimum of expensive tooling.
In accordance with this invention, inaccuracies which may result from an accumulation of tolerances are either compensated for, or are rendered insignificant as a result of the meter construction, while maintaining many advantages which permit rapid assembly and manufacture of a low cost meter.